The aims of this proposal are the study of two new gastrointestinal influences on serum calcium homeostasis in the rat. The first relates to the importance of the stomach or a gastric factor in mediating the hypocalcemia induced by gastrin and histamine. The gastric factor, we feel, may be more important than the thyroid release of calcitonin under these circumstances in the development of hypocalcemia. The second part of the study deals with extraction, purification and physiological importance of a new calcium-elevating peptide from the pancreas. This was first recognized in commercially prepared insulin and has now been partially purified from pig pancreas.